1. Field of the Invention
This invention relates to flow switches, that is to switches for detecting flow of a fluid.
2. Description of the Prior Art
In certain applications, it is necessary to detect that a fluid such as a liquid is flowing and to provide an electrical signal dependent thereon. One such application is in shower systems having a pump for providing sufficient pressure to operate the shower, in installations providing an inadequate head of water. Depending on whether the pump is operating or not, and whether or not the water tap has been opened, flow of water may or may not be taking place, and it is necessary to provide an indication of flow to ensure proper control and to prevent possible damage to the installation.
It has been proposed to provide a flow switch in the form of a housing within which a magnetized float member can move between one position in which flow is either not occurring or is being initiated from an undesired direction, and another position to which the float member is moved by fluid flow from a desired direction, the other position allowing fluid flow through the flow switch. A magnetically-responsive switch, such as a reed switch is positioned to detect the position of the float member such that a flow detect signal is provided when the float member is in the other position. Examples of such flow switches are disclosed in UK Pat. Nos. 1 360 225, 1 496 601 and 1 604 247.
A problem with the previously-proposed flow switches is that the design has led to the float member and corresponding parts of the internal bore of the flow switch providing a significant obstruction to the fluid flow. This is particularly disadvantageous since, in many applications of the flow switch, the source of fluid pressure may be unreliable and periodically insufficient; in such a case, it is clearly undesirable to cut down the available pressure still further by obstruction of whatever flow could otherwise be obtained.
Another problem with some previously-proposed flow switches is that the design effectively provides a seal against reverse flow, the float member seating against a corresponding surface of the bore. Whereas in general it is not required for the flow switch to allow a substantial fluid flow in the reverse direction, in many applications it should be possible for fluid to return to the inlet side of the flow switch, in other words a certain degree of fluid seepage should be permitted. Otherwise, for example, a column of water may be trapped above a vertically-disposed flow switch which is closed, and if this column of water is tall enough, it will affect operation of the float member on which it is acting.
UK patent application Ser. No. 2 189 648 A discloses an offset-type flow switch in which the inlet and outlet passages are not collinear. The float member is disposed in an extension of the inlet passage and moves as a result of fluid pressure to expose a slot between the inlet and outlet passages. The offset nature of the arrangement means that the flow switch cannot readily be incorporated in an existing installation. The inlet and the outlet connections must be provided in a correspondingly offset manner.